An autotransformer is often used to step-up or step-down voltage. It usually consists of one or more windings wound on a core. A typical single phase autotransformer includes first and second end terminals or taps and an intermediate tap at which an output voltage is developed. During operation, electrical energy is transformed into heat energy due in large part to copper losses, eddy currents and hysteresis losses. Excessive heating of the autotransformer can cause adverse results such as loss of power and damage to the autotransformer. The prior art discloses attempts to obviate this problem with efforts to cool transformers or parts thereof. Unfortunately, the prior art devices often are not entirely satisfactory. In some instances the cooling systems are too complicated, expensive or inefficient in cooling both the core and windings. In other instances, the device is not capable of performing properly under severe conditions, such as where a transformer is located in a device which is subjected to conditions of yaw, pitch and roll.
Moore, U.S. Pat. No. 3,195,085, discloses one prior art system in which cooling ducts in a foil or sheet wound transformer are formed by a series of holes placed in the sheet. The sheet is wound to form a coil, and the holes in the sheet overlap and form a cooling duct. The ducts which are formed extend radially outward from the interior of the structure. No elements or means are disclosed in this patent for cooling both a core and separately wound wires or groups of wires wrapped around the core.
German Patent No. 2,218,659 discloses a cooling system which includes multiple, axial channels disposed concentrically around the core that run parallel to one another and are between the individual, concentric windings. The parallel channels are formed by winding the coils on coaxial formers of increasing diameter that are placed around the core and supported radially by spacers. No provision is made for the radial flow of coolant between individual, spaced apart groups of windings.
United Kingdom Patent No. 26,251 discloses a device which is cooled by the radial flow of coolant between groups of windings and axial flow along the core. However, this device uses a plurality of radial insulating strips placed between the groups of windings to provide a space between the primary and secondary windings.
Other patents, such as Swiss Patent Nos. 46,798 and 249,488 and Fevrier et al., U.S. Pat. No. 4,675,637, disclose internal channel systems which are limited to either cooling the transformer's core or the windings.
What is desired is a relatively inexpensive cooling system for an autotransformer whereby both the core and the windings are cooled. Further, it is desired to utilize a minimal number of components to achieve the desired cooling. Moreover, it is desired that the autotransformer device utilize a cooling system which is adapted to withstand and operate under stringent conditions, such as where the device is subjected to multidirectional movements and forces.